Currently, there is increasing demand for use of radio transceiver devices in mobile communications and the like; Improvements in communication quality and reliability are desired more than ever. As for radio transceiver devices of a millimeter-wave band (e.g. 60 GHz band), in order to simplify circuit configurations and reduce costs, what is proposed is a radio transceiver device of a direct conversion type that is designed to downconvert or upconvert the 60 GHz directly to a baseband. In general, such a radio transceiver device includes an amplifier, which amplifies a high-frequency signal, a mixer circuit, and a local oscillator. Among the above components, a signal from the local oscillator that generates a carrier signal influences the characteristics of the radio communication device. Therefore, improving phase noise of the local oscillator is a challenge in realizing a millimeter-wave band radio communication device.
Furthermore, in a radio communication device that uses a digital modulation method, two-phase sine wave outputs are used in a local oscillator: an I-component signal and a Q-component signal, which are different in phase from each other by 90 degrees. For example, if the above signals each are operated as differential signals, four-phase sine wave outputs are required in total. As for the structures of conventional four-phase sine-wave output local oscillators, for example, the following structures are available among other things: a structure that generates a signal that frequency is double an output frequency, and divides the frequency of the signal to offer four-phase outputs; a structure in which two two-phase sine-wave output oscillators are prepared and used in combination; and a structure in which a polyphase filter is used. It is technically difficult to realize any of the above structures because of problems such as I/Q mismatching.
As an oscillator, an injection-locked oscillator is available. For example, what is disclosed in Patent Document 1 is an injection-locked oscillator that oscillates at a frequency that is in synchronization with and an integer multiple of an injected reference frequency signal. If the phase noise of the reference frequency signal is low, it is possible to keep low the phase noise of an output signal of a frequency that is in synchronization with and an integer multiple of the reference frequency signal.
As for a radio transceiver device of a direct conversion type that does not require calibration for a mismatch between an I-component signal and a Q-component signal, for example, a radio transceiver device disclosed in Patent Document 2 is available. In this case, local oscillators are provided at a transmitter side and at a receiver side. Transmission takes place after a pilot signal is added at the transmitter side. The pilot signal is extracted at the receiver side. The signal is compared with template data that is prepared in advance. A shift adjustment of a 90-degree-shift phase shifter is made so as to be within an error range, so that the phase is adjusted to correct an I/Q mismatch.